Building codes in the United States place certain fire restrictions on cellular plastics used in construction. Sheathing products must at least meet the Class II requirements of the ASTM E-84 test: flame spread xe2x89xa675 and smoke xe2x89xa6450. Class I E-84 criteria (xe2x89xa625 flame spread and xe2x89xa6450 smoke) are desirable, but not specifically called for in the building codes.
Roofing products, in addition to other tests, must meet the Factory Mutual Class I Approval as described in Factory Mutual Procedure 4450/4470. An important component of the Factory Mutual 4450/4470 procedure is the so-called FM Calorimeter test (hereinafter referred to as the context requires as the Calorimeter test, Calorimeter testing, or Calorimeter). In the Factory Mutual (FM) Calorimeter test, a 22.5 ft.2 section of the particular roof construction is subjected to a heptane-fired flame for thirty minutes. According to the FM 4450 standard, the intended sample exposure is 1650 BTU/min./ft.2 The heat release rate and total BTU content of the sample is determined and compared to the acceptance criteria. The FM Calorimeter test reports the peak heat release rates for the worst 3-minute, 5-minute, and 10-minute periods, as determined from the time/temperature curve. The average heat release rate, equal to the sample (total BTU/448), is also reported and used as a pass/fail criteria.
Approvals obtained under FM 4450/4470 are specific to the roof construction tested. The approval is limited to a minimum thickness of the insulation, and to the particular construction. For years, the xe2x80x98worst casexe2x80x99 construction has been the xe2x80x984-ply glassxe2x80x99 built-up roofing (BUR) system. In this construction, the foam insulation is applied directly over a fluted steel roof deck. The steel decking in the test sample is not continuous. It is composed of two pieces, overlapped by about xc2xcxe2x80x3 and not secured with stitch screws. The top surface of the foam insulation is then mopped with Type 3 asphalt. Seven overlapped pieces of glass ply-sheet are applied with alternating moppings of asphalt to secure the ply sheets. A final asphalt mopping or xe2x80x98flood coatxe2x80x99 is then applied to the top surface of the roof deck. Starting in 2001, FM instituted routine weighing of the roof deck to determine the total amount of asphalt applied. The asphalt application rate is reported by FM to be included in any subsequent approvals from the particular sample. Asphalt application rates are critical because our results indicate that there is not enough BTU contribution available from a typical 1.5xe2x80x3 PIR foam board to fail the Calorimeter test.
Prior to this invention, the results of Calorimeter testing by others has been made available to see if such information would enable the development of superior test method. Such Calorimeter testing has included diagnostic tests, including the use of test decks using commercially-produced cover-boards and no asphalt. Also made available as background information were the results of extensive determinations of the total available BTU content of all roof deck components, using bomb calorimetry. Such data, summarized in Table 1, allows the researcher to calculate the approximate total BTU content of any Calorimeter test deck. The BTU content of each component is shown in BTU/lb. as well as the total pounds and BTU typically installed on the 22.5 ft.2 test deck. The BTU content should be determined for each foam formulation, and for any alteration in type or supply of the deck components.
Also made available was information based on BTU determinations of the char remaining after the Calorimeter test, and calculations of the net BTU consumption in the Calorimeter. It had been found that typically the total BTU content of the deck, as reported by the Calorimeter, is 10-35% higher than the available BTU as determined by the bomb calorimeter, even when it is assumed that the entire 22.5 ft.2 of the Calorimeter test deck is consumed. Actual measurements indicated that approximately 19 ft.2, or 85% of the total Calorimeter test deck area, participates in the test. This is in contrast to the 16 ft.2, or 71%, of the total test deck are assumed in the Calorimeter test procedure and calculations.
Results of, and conclusions from, investigations on the reproducibility of the Calorimeter test were also provided as background information. These investigations had been conducted with repeat tests of the same board in identical constructions. The data indicates that 1 standard deviation for the average BTU/ft.2 min. for a typical xe2x80x984-ply glassxe2x80x99 BUR construction is on the order of 50 BTU/ft.2 min. The 2"sgr" (95%) confidence interval then is 285+/xe2x88x92100 BTU/ft.2 min.
Recent measurements show that temperatures of 1500-1600xc2x0 F. (820-870 C) can develop on the underside of the steel deck during the Calorimeter test. Similar temperatures have been recorded for research Calorimeter tests, using constructions that employed a cover board and no asphalt. The temperatures recorded as part of the Calorimeter test were measured in the exhaust flue by an array of 12 thermocouples and averaged. Measurements showed that the actual exposure temperature of the test deck can be up to 400xc2x0 higher. Temperatures are lower in the exhaust flue of the Calorimeter due to mixing of stratified airflow.
Under the test deck exposure conditions, the ideal roof insulating material should provide a thick intumescent char, with minimal cracking, that would protect the asphalt in the BUR test sample. The insulation in the test sample is composed of four separate pieces that are butted together in the form of a square when viewed from above. For this reason, the ideal insulation also will not shrink or contract when exposed to the test conditions. Shrinkage will open up seams at the butt-joints and allow melted asphalt to flow through, eventually reaching the inside of the firebox and contributing to the observed total BTU. Laboratory screening tests focus on three key attributes of the foam: thickness retention, lateral shrinkage, and char integrity.
Several prior laboratory flammability methods are available to the researcher. The most common and easiest screening procedure is the so-called xe2x80x98hot-platexe2x80x99 test. The roof insulation product is cut to 4xe2x80x3xc3x974xe2x80x3 samples and placed on a pre-heated laboratory hotplate. Samples may be from faced production boards or from un-faced laboratory foams. A 900 gram weight maintains contact of the foam on the sample stage and prevents curling. The sample is heated on one side in the same manner as in the Calorimeter. Typically the hotplate is heated to 850xc2x0 F. and the sample is exposed for 30 minutes. In fact, the temperature should be 870xc2x0 C. (1598xc2x0 F.) to simulate the actual exposure in the Calorimeter. Commercially available laboratory hotplates will generally not reach the same temperatures as the Calorimeter. Historically, a hotplate temperature of 800-850xc2x0 F. has been used and correlated empirically to the Calorimeter.
Prior to October, 1999 this correlation served fairly well. Under the old Calorimeter correlation, results of 15% or less thickness loss in the hotplate are considered good and the material is a good candidate for Calorimeter testing. Results of 16-25% thickness loss in the hotplate are considered marginal candidates for Calorimeter testing. Those boards with  greater than 25% thickness loss in the hotplate are generally not considered for Calorimeter testing.
Statistical treatment of hotplate data showed that the 95% confidence limit is fairly broad. For this reason, hotplate data has traditionally been used only as a screening method. In spite of the large error bars associated with hotplate results, trends became obvious when large data sets of similar density foams were compared for different flame retardant combinations.
Weight loss and dimensional change have generally not been used as criteria for hotplate screening of materials for Calorimeter testing. Wide variation in thickness change is seen with samples that have substantially the same weight loss. Dimensional stability has been re-evaluated with regard to Calorimeter performance and the new method of the present invention. Of particular interest is any lateral shrinkage of the foam that will open the main seam in the Calorimeter test and allow molten asphalt to reach the firebox.
After October 1999, experts in this field detected an apparent base-line shift in the Calorimeter. Identical boards from the same bundle were tested in the FM Calorimeter and produced substantially different total BTU results. The total BTU reported by the Calorimeter was approximately 54% higher in the more recent tests ( less than 115,000 vs.  greater than 177,000 BTU). This outcome was found with manufactured PIR boards produced both with 141b and hydrocarbon blowing agents. One result of the shift was that a new correlation between the laboratory methods and the Calorimeter had to be established. It was also desirable to develop new laboratory methods that were better predictors of Calorimeter performance.
Accordingly, the provider of the foregoing background information expressed the desire for the development of a new, more definitive laboratory test. A first attempt at fulfilling this desire was a method based on use of a vented oven capable of reaching 1200xc2x0 F. (650xc2x0 C.). While giving a good first indication of char formation, concern remained that the method did not offer information on the large-scale cracking behavior of the foam char. In addition, the vented oven exposes the sample to heat on all six sides, unlike the Calorimeter. Thus a need exists for a new test method and new apparatus capable of more accurately predicting how foam test specimens will behave in the required (and expensive) Calorimeter test.
The present invention is deemed to fulfill the foregoing needs and desires in an efficient and effective manner. At the same time it avoids the shortcomings noted for the vented oven test procedure.
The methods of this invention involve:
a) applying heat to the underside of a heat-conductive plate on which are disposed (i) a test specimen of the cellular plastic having a top surface and a bottom surface, (ii) a plurality of spaced-apart heat sensing devices disposed below the specimen and in direct or substantially direct contact with the plate, one such heat sensing device being substantially centrally disposed relative to the plate and serving as the setpoint sensor, and (iii) a plurality of spaced-apart heat sensing devices disposed above the specimen and in direct or substantially direct contact with the top surface of the specimen, one said heat sensing device being substantially centrally disposed relative to the top surface of the specimen, the sensing devices being adapted to provide signals convertible into information regarding the temperatures at their respective locations; and
b) at a preselected elevated temperature as sensed by said setpoint sensor, determining the time for the sensors of (iii) to sense a rise in temperature and/or to reach a preselected temperature at or below the preselected elevated temperature sensed by said setpoint sensor.
Apparatus of this invention comprises:
a) a heat-conductive plate having upper and lower surfaces, each surface having a central location;
b) a heater centrally or substantially centrally disposed relative to said central locations of the plate;
c) a plurality of heat sensing devices adapted, when a specimen of a cellular plastic is placed on said plate, to be disposed in spaced-apart locations below the test specimen and in direct or substantially direct contact with the plate and to transmit signals convertible into information regarding the temperature at the location of the heat sensing device;
d) a plurality of spaced-apart heat sensing devices adapted, when a specimen of a cellular plastic is placed on said plate, to be disposed in spaced apart locations above the specimen and in direct or substantially direct contact with a top surface of the specimen, and to transmit signals convertible into information regarding the temperature at the location of the heat sensing device;
e) a thermally insulated housing including a thermally insulated cover, said housing and said cover when closed being adapted to encase said plate, a specimen of a cellular plastic when placed on said plate, and said heater entirely or substantially entirely within the confines of said housing and cover;
f) a microprocessor adapted to receive signals from the respective heat sensing devices, and to convert said signals into signals corresponding to temperatures sensed by the respective sensing devices; and
g) a display device, adapted to receive the signals from said microprocessor and to display information indicative of the respective temperatures sensed by the respective sensing devices;
wherein f) and g) can be separate units or a single combined unit.
The heater used is preferably a thermally insulated radiant heater capable of heating test samples through the plate to temperatures of up to about 870xc2x0 C. (1600xc2x0 F.) or higher, temperatures which are not achievable by use of conventional hot plates.